1. Field of the Invention
The present invention relates to a fuel injection structure for an internal combustion engine with a straight intake port defining passage.
2. Description of the Prior Art
An internal combustion engine with a straight intake port defining passage which extends straight in an oblique and upward direction from the vicinity of a valve head of an intake "valve so as to define an intake port at a downstream end of the intake port defining passage is disclosed in, for example, Japanese Patent Publication 62-28368. As illustrated in FIG. 10 (Prior Art), a fuel injection valve is mounted to such a straight intake port defining passage with an angle .theta..sub.1 defined between an axis of the straight intake defining passage port 2 and an axis of the fuel injection valve 4. In the arrangement, fuel is injected with angle .theta..sub.1 with respect to the direction of the intake air flow.
However, there are the following problems in the above-described fuel injection. First, a great amount of fuel collides with and adheres to a bottom surface of the intake port defining passage and the response characteristic of the engine is degraded. Secondly, in accordance with changes in the load or in the flow velocity of the intake air, the direction of the injected fuel changes upward and downward (in direction x of FIG. 10), and an optimum direction of the fuel injection cannot be determined. This means that the fuel is injected in non-optimum directions in almost all operating conditions.